Hepatitis A virus has been successfully adapted to growth in African green monkey kidney tissue culture. Over 28 serial passages have been achieved, and infectivity titers as high as 100 million infectious units per ml of cell concentrate have been achieved. The virus is predominantly cell-associated and does not produce cytopathic effects (CPE). It was attenuated for chimpanzees after 10 serial tissue culture passages; reevaluation of the virus in chimpanzees after 20 tissue culture passages indicates the virus infectivity and attenuation have remained the same as at passage level 10.